The following selection is taken from "Saga in Steel and Concrete:
Norwegian Engineers in America" by Kenneth Bjork published by the
Norwegian-American Historical Association (NAHA) in 1947. The volume is
still available from NAHA at http://www.naha.stolaf.edu where you will
also find the first 33 volumes of Studies and Records online. This
chapter is published with the kind permission of NAHA. The book this
selection is drawn from is under copyright and permission has been
granted for educational purposes and it is not to be used in any way for
any commercial venture.

The tubes were unwatered by pumps, which were installed in the first
section of the tunnel before it was launched, remaining submerged more
than seven months before they were started. No difficulty was
encountered; the unwatering usually "required 3 hours per tube in a
section, or 6 hours for two adjoining tubes." Hoff explains also:
One object in developing the adopted design, was to reduce the use of
divers to a minimum. Diving is expensive work, and frequently unreliable.
The only physical labor performed by divers was the temporary attaching
of the steel tubes to the grillage in the trench, the bolting up of the
joints of the tube sections, and the disconnecting of the air cylinders.
In other respects, divers were only used as "eyes to see with," that is,
as inspectors to report conditions. The total cost of diving at Detroit
was only about one-half of 1% of the total cost of the river tunnel.
Commenting on workers and accidents, Hoff states that "the construction
of the whole river section was singularly free from accidents, not a
single fatality occurring in connection with the river work --- a
striking contrast to the general experience when compressed air and
shields are used. It may be of interest to note that three of the largest
concerns in the country writing Employers' Liability Insurance offered to
give protection at about one-third the rate they charged for tunnel work
done under compressed air."
Hoff estimates, in discussing the advantages of his tunnel, that about
$2,000,000 was saved at Detroit because of the small labor cost involved;
and this was not offset by a greater cost of materials. He argues, too,
that a capitalized saving in the railroad's annual cost of operation was
effected, since his tunnel provides a roadbed some 15 feet higher than
would have been the case with a deeper shield-driven tunnel - thus
reducing the vertical lift of tonnage. About 1,000 feet of approach
tunnel on the Canadian side was also saved, and about 750 feet on the
American side.
"After two years of constant effort and sacrifice of health to make this
new and untried method of subaqueous tunneling a success," Hoff
concludes, "it was a source of the greatest regret to the writer that he
was unable to remain with the tunnel and witness its completion;
circumstances beyond his control made it necessary for him to retire from
the contracting firm in October, 1908, after Section No. 6 had been sunk,
and after practically all problems presenting themselves with this work
had been solved." {14}
How Hoff worked has been described by one of his assistants at Detroit.
The tunnel plan "occupied many pages in his neatly-kept book of sketches
and calculations. Every detail was worked out, not only those pertaining
to the strength of the finished structure but also every little accessory
and arrangement in connection with the execution of the work. So when the
job was turned over to the construction forces everything dovetailed; it
all worked out as calculated, with no lost time. It was a complete
success." No detail, however small, was overlooked by Hoff, and his sandy
hair and keen blue eyes behind gold rimmed glasses became a familiar
sight to the tunnel workers during the months that he supervised
construction at Detroit. {15} The sudden disappearance of Hoff from the
tunnel scene was caused by a sharp clash he had with Butler Brothers.
Hoff maintained that, after the success of his plans had been
demonstrated beyond all doubt, disagreements about the disposal of
machinery resulted in an effort by his partners to deprive him of his
predetermined share of the company's financial return from the project.
This share amounted to one fifth of the profit, which would have been
about $1,500,000. When Hoff's salary, too, was cut to very little, he
brought suit against Butler Brothers. Whatever the legal or other merits
of his claim, a financial settlement was made out of court. One result of
Hoff's troubles at Detroit was that during his second great tunnel
undertaking he made all necessary arrangements with a bank, kept the
financial strings in his own hands, and realized about $1,000,000 as his
share of the profit. {16}
IV
In the various articles describing the Detroit River Tunnel, Hoff's name
was mentioned only in passing. With the beginning of his next project, a
subway tunnel under the Harlem River in New York, it was given a
prominent place. {17} Now a member of the contracting firm Arthur
McMullen and Hoff Company, he was made consulting engineer for the Harlem
Tunnel; his firm received the building contract and his patented method
of tunneling was employed." {18}
The Harlem River borders Manhattan Island on the north. The new tunnel,
at Lexington Avenue and One Hundred Thirty-fifth Street, crosses the
river where it is some 600 feet wide and 26 feet deep at low tide.
Several factors called for the trenching method. It was not permissible
to block navigation on the river, and therefore open cofferdams and
pneumatic caissons, which tend to obstruct the channel, could not be
used. The thin roof of the river bed and the extremely soft ground under
the river, it was believed, would have made shield tunneling difficult.
These and other factors called for a method different from the customary
one, "and eventually the sunken tube method was adopted on considerations
of safety, rapidity, economy and convenience, and it was built by a
modification of the design and method first used by Olaf Hoff . . . under
the Detroit River at Detroit, Michigan." {19}
The Harlem River Tunnel, 1,080 feet in length, is composed of nearly
equal sections containing four tubes instead of two as at Detroit. These
tube sections were built on shore, floated into place, sunk, and bolted
up under water as in the first undertaking. Similarly, too, concrete was
poured through tremies and the tubes were unwatered in the manner
described by Hoff. Little that was basically new was added in the Harlem
Tunnel, but it nevertheless utilized a number of improvements in
construction and proved the adaptability of the trench-and-tremie methods
to this location. Each four-tube section was assembled on a staging about
one mile from the tunnel site. When it was completed and ready to be
sunk, narrow scows were placed between the rows of piling that made up
the staging. When the tide rose, the scows lifted the tunnel section from
its staging and towed it into the river's stream. The scows were then
,scuttled and the section left afloat to be towed by barges in the usual
fashion to the place where it was to be sunk.
A section was first lowered in the middle of the river, rather than at
the shore, and half of the river was closed to navigation. At Detroit the
first section had plunged endwise instead of settling evenly, despite the
use of buoyancy cylinders. At the Harlem River, the sections had, in
addition to the cylinders, partial bulkheads placed on the heavier ends
and extending halfway down from the upper part of two of the tubes. As
water poured into the tubes, the heavier end of the section tipped
downward until the bulkheads touched water, whereupon the air trapped
back of the bulkheads buoyed up the lighter end and the section leveled
off. The air was then allowed to escape through a hose leading to one of
the barges. When all but about a foot of the section's top had submerged,
the tubes sank abruptly until the buoyancy cylinders, which were strapped
at the ends, made contact with the water. When water was admitted into
the chambers within the cylinders, the tunnel piece sank beneath the
surface; derricks, which then took command, lowered it slowly and
accurately into place on bents which had been laid in the trench on the
river bottom. The sections, it is said, came within a fraction of an inch
of true position. {20} The diaphragms of steel, which held the four tubes
together during the sinking process, then provided the necessary
reinforcement for the concrete that was later poured around the section.
Following the successful completion of the Harlem Tunnel in 1915, Hoff
continued to work as before on problems having to do with subway, tunnel,
harbor, and bridge construction. He was chief consultant to the Cunard
Company when it proposed to construct a steamship terminal in the port of
New York, and served in a similar capacity with the New York Central
Railroad when the A. H. Smith Memorial Bridge was designed and built
across the Hudson at Castleton, New York. When the arch bridge of the
Michigan Central was thrown across Niagara River near the falls, he was
again called in as consultant. Studious and inventive, he made invaluable
contributions in connection with submarine pile driving, the general use
of reinforced concrete, floor construction, and numerous other structural
features. Varied and significant as his many undertakings were, none
matched his performance at Detroit in working out designs deemed by him
essential to constructing a tunnel in a prepared trench." {21} Hoff died
in December, 1924, honored as a great and original engineer.
V
Just as Hoff's name is identified with the sunken-tube method of
tunneling, so Ole Singstad's is associated for all time with the special
tunnel that was developed to carry the automobile. Tunnels for the use of
vehicles are of recent origin, the first of importance being the
Blackwall Tunnel under the Thames at London, which was opened to traffic
in 1897. Others to be built before the extensive use of automobiles were
the Glasgow Harbor Tunnel (1895), the Elbe Tunnel at Hamburg (1910), and
the Rotherhithe Tunnel under the Thames (1908). The Holland Tunnel in New
York was the first of any size or significance built to care for the.
needs of present-day motor vehicles. {22} As a result this tunnel
presented new and difficult problems, the solution of which put
Singstad's name on the roster of modern pioneers. Singstad designed the
Holland Tunnel, worked out its unique system of ventilation, completed
its construction as chief engineer, and operated it for two and a half
years after its completion. In subsequent years he acted either as chief
engineer or as consultant in connection with the most important vehicular
tunnels that were constructed.
The Holland Tunnel and its successors in New York play such a vital part
in the life of America's greatest port city that a brief discussion of
these tunnels seems essential here. Prior to the building of the first
vehicular tunnel under the Hudson River, Manhattan was connected with New
Jersey, lying to the west, only by electric-car and train tubes and about
fourteen steamboat ferries. With no bridges for many miles up the river,
ferries were overworked to such a point that it was necessary on Sundays
and holidays for motorists to wait for hours before crossing the Hudson.
And weekdays were only slightly better. As is generally known, the
financial and wholesale districts of New York are concentrated in lower
Manhattan. Strangely enough, this nerve center was --- and still is ---
linked with the Jersey side by only six railroad and electric-car tubes.
{23} In Singstad's own words:
[When] it is borne in mind that on the Jersey side of the river are the
terminals of eight trunk line railroads, that the greater part of the
population of the metropolitan district is located to the east of the
Hudson River, that most of the steamship terminals, both for coastwise
and foreign shipping, are located either in Manhattan or in Brooklyn, and
also that there are large population centers in New Jersey immediately
west of the river, it is quite evident that, when a comparison is made of
the volume of traffic crossing the Hudson River with that crossing the
East River, the absence of vehicular traffic facilities has been a great
hindrance to the development and free movement of the traffic between
Manhattan and New Jersey. It was this pressing need . . . which prompted
the two states to create the commissions which are now constructing the
Holland Tunnel . {24}
Earlier efforts had been made to tunnel under the mile-wide Hudson. In
1874 a western promoter, De Witt C. Haskins, came to New York, raised the
necessary capital, and began the first attempt to pierce the river's soft
bed. Legal difficulties postponed the project for five years, but finally
in 1879 work was begun. Using compressed air but no shield, Haskins
failed utterly. Walls and ceilings gave in, 23 men were killed --- and
the tunnel was abandoned. Eventually, in 1908, it was completed as the
McAdoo Tunnel under different engineers. {25} Next, a large English
engineering firm sent experts to New York to see what might be done in
the way of a tunnel. Plans were drawn up but never executed; the cost was
too great. {26}
A bridge had long been considered both feasible and desirable. As early
as 1868, Singstad informs us, the states of New York and New Jersey
granted charters to a private corporation to build a bridge across the
Hudson. Nothing came of this plan. In 1906, at the instance of
public-spirited citizens, each state appointed a commission to study the
possibility of a bridge to be built with public funds. These commissions
concluded in 1913 that it would be economically impracticable to build a
bridge where the traffic needs were greatest. They then began a study of
the possibilities of a tunnel. {27}
The bridge and tunnel commissioners had made sufficient progress by 1919
to justify the appropriations of $1,000,000 made by each state to begin
plans and actual construction of a tunnel. Clifford M. Holland, who was
appointed chief engineer of the joint commissions, recommended in 1920
that twin tunnel tubes, each of which would handle two lines of one-way
traffic, be constructed under the Hudson. {28}
The plan for a bridge had been discarded for a number of reasons. It was
evident, in Singstad's opinion, "that a tunnel is a more suitable and
economic type of structure than a bridge, where the conditions are
similar to those existing at the location of the Holland Tunnel, and, in
fact, for entire Manhattan Island below Central Park." These conditions
consist of a waterway over 3,000 feet wide between pierhead lines, low
riverbanks, and high land values.
If a bridge were to be built at this location, the cost would be
excessive due to the long span, the expensive foundations due to the
great depth to rock . . . and the expensive approaches. A bridge would
have to have a clearance of from 180 to 200 feet above mean high water,
and its approaches . . . would have to be carried inland as far as
Broadway. . . . A long bridge approach also would be detrimental to the
real estate values under and in the vicinity of the bridge. With a tunnel
it is only necessary to go down a distance of less than 100 feet below
mean high water with the roadway due to navigation requirements, so that
the approaches would be about one-half as long as those for a bridge. . .
. The tunnel further has the advantage that it does not depreciate real
estate values in its immediate vicinity, as there is no surface evidence
of the structure except in the short distance from the portal to the
point where the roadway meets the street surface. {29}
The decision made in favor of a tunnel, Holland lost no time in
approaching Singstad. They had known each other from the time the latter
was designing engineer of rapid-transit tunnels; Holland was construction
engineer on the same projects, and Singstad's abilities had impressed
him. Singstad had ,acquired a broad experience and skill which the
brilliant Holland, now chief engineer for the new tunnel, was quick to
seize upon. One day in 1919, the story goes, Holland telephoned Singstad
and asked him to call at his office. Holland, himself only thirty-six
years old, invited the young Norwegian to be his engineer of design. {30}
After some hesitation Singstad accepted the proffered post. In 1924
Holland died and was succeeded as chief engineer by Milton H. Freeman.
Three months later Freeman died, and Singstad, who had designed the
tunnel, carried it to completion in 1927 as chief engineer.
The man who made history in designing and completing the Holland Tunnel
and who is now the dean of all tunnel engineers was born at Lensvik in
1882. Following his graduation from Trondhjem's Technical College in
1905, Singstad had left without delay for the United States. In New York
he immediately found work with the Central Railroad of New Jersey. He
left in the next year for Norfolk, Virginia, where he designed railroad
structures and assisted in rail and bridge construction for the
Virginian Railway. Returning to the East, he took a position with the
Hudson-Manhattan Railroad, preparing designs for work on Hudson River
tunnels during 1909-10. He also designed rapid-transit subways and
tunnels in New York, in Brooklyn, and under the East River, remaining for
seven years in charge of this work and working with Holland for the
Public Service Commission of the first New York district. After
establishing a sound reputation as a first-class tunnel engineer,
Singstad served during 1917-18, in charge of structural design, with the
Chile Exploration Company, and in 1918-19 with Barclay Parsons and Klapp,
in charge of laying out and estimating a rapid-transit system for
Philadelphia. While with the latter firm, he made preliminary designs and
estimates and reported on a vehicular tunnel under the Delaware River.
{31}
A great deal has been written about the Holland Tunnel, for it began a
new chapter in engineering history. {32} Much of what has been written is
in technical language and has no great interest for the layman. A few
general facts, however, seem to be pertinent here. The new project cost
about $48,500,000, each state paying half of the total expense. The
tunnel connects Twelfth and Fourteenth streets in Jersey City with the
borough of Manhattan at Canal and Varick streets and Broome Street, and
operates on a toll basis. The tunnel actually consists of two separate
tubes, each with an exterior diameter of 291/2 feet; the northern one
serves west-bound and the southern serves eastbound traffic. Between
portals it is 8,463 feet long. {33}
In planning the tunnel, we are told, two types of construction were
considered --- the trench-and-tremie, together with other trench methods,
and the well-known shield technique. "On account of the heavy river
traffic, the soft character of the river bed, and the intensive use of
the water front, the shield method was considered the safer and more
economical." The tunnel was constructed by first sinking shafts as
pneumatic caissons on shore. Shields were started from these shafts, two
from the New York side and two from the Jersey side, the shields meeting
under the river. "On their way the shields passed through a second set of
caissons, which had been sunk in advance of the approach of the shield to
serve as foundations for the second set of ventilation buildings located
in the river back of the pierhead line. On the New Jersey side, two
additional shields were started westward, to carry the construction back
to points where excavation by the open-cut method could be successfully
carried on."
Work in compressed air required pressure up to 47½ pounds per square inch
above atmospheric pressure, involving "756,000 decompressions of men
coming out of the compressed air workings." The job was finished with
only 528 cases of "bends," and none of these cases resulted in death.
{34}
However interesting the detailed designs of the tunnel itself, the tools
employed, and the problems inherent in driving a shield for tubes of
great diameter, these must give way to another feature =the novel system
of ventilation which is Singstad's unique contribution and a pioneering
feat of real significance. {35} Fortunately, Singstad has told in detail
the story of how this system evolved under his direction. Because of its
importance, we quote at length from a paper presented by Singstad before
the World Engineering Congress at Tokio in 1929. {36} In this paper is
explained how the chemist and physiologist came to the aid of the
engineer in overcoming one of the greatest barriers to underground
travel.
The extreme length of the tunnel tubes, each with a 20-foot roadway
"providing for two lines of traffic in the same direction in each tube
with an estimated total capacity of 3,800 vehicles per hour," and the
assumption that all traffic would be propelled by gasoline engines
presented a problem in ventilation which, "both in character and
magnitude, had no precedent."
It was therefore necessary to establish original fundamental data on
which to base the ventilation plan, as it was fully realized that the
success of the tunnel project was dependent on the ability of the
engineers to devise a system of adequate ventilation under all traffic
conditions. The problem was studied under three main subdivisions:
1.Amount and composition of exhaust gases from motor vehicles;
2.Physiological effects of exhaust gases from motor vehicles;
3. Method and equipment required to provide adequate ventilation.

<14> American Society of Civil Engineers, Transactions, 74:361-373
(December, 1911).
<15> Guttorm Miller of Detroit to the writer, January 11, 1941. For a
sketch of Hoff, see Flynn Wayne, "Olaf Hoff-His Work," in National
Magazine, 38:51 (April, 1913).
<16> Information furnished by F. J. Vea of Madison, Wisconsin.
<17> Subway Tunnel under Harlem River," in Engineering Record, 68:556
(November 15, 1913). See also Wayne, in National Magazine, 38: 51.
<18> Patent numbers 907,356, subaqueous tunnel (December 24, 1908) ;
907,357, method of sinking subaqueous tunnels (December 24, 1908); and
972,192, apparatus for subaqueous pile driving (October 11, 1910).
<19> Frank W. Skinner, "The Harlem River Subway Tunnel, New York," in
Engineering (London), 104: 32 (July 13, 1917). Skinner's detailed report
of the tunnel is carried in serial form, appearing also p. 83-87 (July
47, 1917). See also Nordisk tidende, August 22, 1914.
<20> Scientific American, 109: 244 (September 27, 1913). See also vol.
108, p. 486 (March 29, 1913).
<21> Asked for an appraisal of the Detroit job, Carl H. Stengel, New York
consulting engineer and former partner of W. S. Kinnear, said, "Mr.
Wilgus originated the idea. . . . Mr. Hoff developed a practical means of
accomplishing the results of the Wilgus idea"; to the writer, September
11, 1945.
<22> S. A. Thoresen, "Constructing the Detroit-Windsor Tunnel," in Civil
Engineering, 1:613 (April, 1931); Ole Singstad, "Ventilation of Vehicular
Tunnels," in World Engineering Congress, Proceedings, 9:381-399 (Public
Works, part 1-Tokyo, 1931).
<23> Frank W. Skinner, "The Holland Vehicular Tunnel, under the Hudson
River," in Engineering (London), 124: 601-606 (November 11, 1927). This
article, which is continued in the issues of November 25 (p. 667-671) and
December 9 (p. 785-788), is the most exhaustive study on the subject to
be found in the technical journals.
<24> Ole Singstad, The Relation of Tunnels and Bridges to Traffic
Congestion," in American Academy of Political and Social Science, Annals,
183:69-71 (September, 1927)
<25> Kirby and Laurson, Modern Civil Engineering, 174; Nordisk tidende,
December 15, 1938.
<26> Nordisk tidende, December 15, 1938.
<27> Ole Singstad, "The Holland Tunnel," in Norwegian-American Technical
Journal, vol. 1, no. 3, p. 1 (September, 1928).
<28> It should be made clear that Holland was the genius of the tunnel
project. A summary of his report to the joint commissions is found in
Engineering News-Record, 84:357-364 (February 19, 1920). Singstad, as
Holland's engineer of designs, was ably assisted by A. C. Davis,
mechanical engineer, and J. N. Dodd, electrical engineer. The more
important parts of Holland's report were approved by a board of
consulting engineers composed of W. J. Wilgus, J. A. Bensel, William H.
Bua, Edward A. Byrne, and J. V. Davies.
<29> American Academy of Political and Social Science, Annals, 133:
73-76.
<30> So Nordisk tidende, December 15, 1938; an interview signed "H.O."
This is the best sketch of Singstad to be found in the Norwegian-American
press.
<31> Norwegian-American Technical Journal, vol. 4, no. 1, p. 12 (April,
1931); H. Sundby-Hansen, in American-Scandinavian Review, 15:360 (June,
1927); Wong, Norske utvandrere, 76; Alstad, Trondhjemsteknikernes
matrikel, 226; Alstad, Tillegg, 63; "H.O.," in Nordisk tidende, December
15, 1938; information supplied by Singstad in May, 1941.
<32> In addition to the articles cited in this chapter, there is a
lengthy unpublished account of the tunnel, written by Ole Singstad, in
the Engineering Societies Library, New York City.
<33> A comprehensive general survey of the Holland Tunnel may be found in
Engineering (London), 124:601-606, 667-671, 735-738 (November 11, 25, and
December 9, 1927). A briefer and less technical account is contained in
Scientific American, 137:201-203 (September, 1927).
<34> Ole Singstad, in Norwegian-American Technical Journal, vol. 1, no.
3, p. 1-3, 10 (September, 1928). For detailed information on work under
compressed air, see Singstad, "Industrial Operations in Compressed Air,"
in Journal of Industrial Hygiene and Toxicology, 18:497-523 (October,
1936).
<35> For other accounts, see "Studies and Methods Adopted for Ventilating
the Holland Vehicular Tunnels," in Engineering News-Record, 98:934-939
(June 9, 1927); and "Ventilating the Holland Vehicular Tunnel," in
Heating and Ventilating Magazine, 23: 79 (August, 1926).
<36> Singstad, in World Engineering Congress, Proceedings, 9:381-399.

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